For producing the graphs, YUI Charts
module is used. The code is using modern Moodle development techniques and
patterns, such as using LESS for producing CSS files and Shifter to compose the
Javascript modules.

You should be able to see all successful login in your site logs. Go to Administration > Reports > Logs and you can the filter by the user you are looking for, choose "download in excel format" or "download in ods format". You can then open them up in your spreadsheet application and filter them by action to only display Logged in user.

Dear Arindam,
Yes, I can find log in Administration > Reports > Logs, but we would like to search the information by week or by month. And now we face the question as same as the link https://moodle.org/mod/forum/discuss.php?d=350237#p1413799 .
So at the same time, we try to find out the related information with you .
Thanks a lot.
Best Regards, Anderson Hsu